1. Field of the Art
This invention relates to a process for producing an aromatic sulfide polymer by subjecting a dihaloaromatic compound to dehalogenation/sulfidation reactions with a metal sulfide. More particularly, this invention relates to a process for producing an aromatic sulfide polymer having a markedly high molecular weight, characterized in that the polymerization reaction is conducted under specific conditions.
In recent years thermoplastic resins having ever increasing thermal resistance have been in demand for electronics parts, automobile parts, etc. Aromatic sulfide polymers may have such properties as to meet such a demand, but the conventional polymers of this class have been of high crystallinity, and, moreover, it has been difficult to obtain those of sufficiently high molecular weight. For this reason, there have been serious problems such as the difficulty of molding these polymers into films, sheets, fibers, etc. and the fragility of the resulting molded products. The present invention provides a novel process for producing a linear aromatic sulfide polymer having markedly high molecular weight to solve these problems.
2. Prior Art
Hitherto the following processes for producing aromatic sulfide polymers have been known.
(1) A process for melting and reacting elemental sulfur, dichlorobenzene and a base such as Na.sub.2 CO.sub.3 in the absence of a solvent (U.S. Pat. Nos. 2,513,188, 2,538,941, etc.).
(2) A process in which an alkali metal sulfide, especially Na.sub.2 S.9H.sub.2 O, is heated in a polar solvent to remove its crystal water, and a mixture of the resulting anhydrous sulfide and dichlorobenzene is subjected to thermal polymerization (U.S. Pat. No. 3,354,129, etc.).
(3) A process similar to the above described process (2) in which Na.sub.2 S.9H.sub.2 O is heated in a polar solvent containing a carboxylate salt caused to coexist therewith to remove its crystal water, and a mixture of the resulting anhydrous sulfide and dichlorobenzene is subjected to thermal polymerization (U.S. Pat. Nos. 3,919,177, 4,089,847, etc.).
As far as we are aware, these processes do not appear to be satisfactory. More specifically, the molecular weight of the resulting polymer according to the above described process (1) is too low, and it is difficult to obtain a linear aromatic sulfide polymer for practical uses. According to the above process (2), a polymer having molecular weight somewhat higher than that according to the above process (1) is obtained, but it is still difficult to obtain a linear aromatic sulfide polymer having satisfactory molecular weight for practical uses. The above process (3) has been developed to increase the molecular weight of the polymer prepared according to the process (2), whereby the molecular weight itself has been considerably improved. By the process (3), however, it is still rather difficult to readily produce films, sheets, fibers, etc. having great toughness in an economical manner with good reproducibility, as far as we are aware.
The difficulty of sufficiently raising the molecular weight in the above process (2) or (3) may be attributed to the following and other reasons. Since, in spite of the fact that the minute quantity of the coexisting water has a very great influence on the increase or decrease of the molecular weight, a process wherein the large quantity of water entering into the solvent from the starting material Na.sub.2 S.9H.sub.2 O is evaporated off by heating in the solvent is adopted:
(a) complete dehydration is difficult, and control of the quantity of the dehydration is also difficult;
(b) with the process in a state wherein a considerable quantity of water content is still remaining, the heavy metal of the reaction vessel is corroded and undergoes dissolution, and the heavy metal ions inhibit the formation of a polymer of high molecular weight; and
(c) during the evaporating of the water content, the sulfur content is also caused, in the form of H.sub.2 S and the like, to accompany the water and is lost, whereby precise control of the sulfur content becomes difficult.
Moreover, a problem encountered in the process (3) is that, since a large number of water-soluble salts of organic acids, especially acetate, are caused to exist in the polymerization system, a large amount of organic acids is admixed with waste water used for treating the polymerization product, which may cause pollution problems. Furthermore, a great expenditure would be needed to remove the contaminated organic acid.